I witnessed my partner's suicide. We met because we had suicidal thoughts and wanted to do it together, but we ended up falling in love in the process. This person was getting better, and I genuinely liked and supported that, but I was becoming increasingly depressed—not because of them, but because I was entering a process of understanding, called the nigredo, though I didn't understand it at the time. So, I broke up with this person to not take them with me to the grave, because I was already thinking of giving up and didn't want them to die just because I gave up on life. That decision of mine was perhaps a mistake, because one day this person called me to say goodbye, and I accompanied their CTB, trying at least to comfort them in their final moments... But after that, I couldn't feel anything anymore. At first, it seemed like things made no sense; my mind struggled to understand for at least four months. There wasn't a desperate pain. After four months, one day I felt the world collapse and an immense pain in my chest.I thought about killing myself, but I thought it would be too easy to run away, and the guilt wouldn't let me commit suicide. I spent a few weeks very sad, not wanting to do anything, but I didn't refuse the thoughts about the one I loved. Even though it hurt, I kept thinking about them anyway. Over time, I began to accept and understand. The guilt I felt started to diminish. As months passed, I began to remember this person with a certain tenderness—it was a bittersweet feeling; it hurt but also relieved. Nowadays, it's something I can remember without pain, even with a certain smile for who this person was to me...
But I don't want to date anyone because I think about suicide, so it would be cruel to date someone and then kill myself later. So I'm avoiding getting into a relationship again.
I don't know if my experience is of any use, but that's how I dealt with it.